Variable ratio of force-enlargement master cylinder of a braking system

ABSTRACT

A variable ratio of force-enlargement master cylinder for a braking system is described. The variable ratio of force-enlargement master cylinder has a cylinder, an outer piston, and an inner piston, in which comprise a plurality of cavities and openings therein. When a force is uniformly applied to the variable ratio of force-enlargement master cylinder, the flow rate of the fluid is preferably changed into a predetermined value by incorporating the cavities and openings located on the cylinder, the outer piston, and the inner piston in a suitable time.

FIELD OF THE INVENTION

[0001] The present invention generally relates to a braking device, andmore particularly, to a variable ratio of force-enlargement mastercylinder for a braking device of a bicycle.

BACKGROUND OF THE INVENTION

[0002] It is well known that a braking force generated from a frictionpad of a rim brake system is used to halt a bicycle by clipping bothwheel edges of the bicycle. However, the dust and moisture are easilyaccumulated on the surfaces of the wheel edges. Such a situationparticularly occurs when the bicycle is ridden in a roadway covered withthe mud or water. Therefore, operating circumstances of the friction padgo from bad to worse, resulting in many problems such as a brakeperformance reduction, or even the safety issues. Moreover, the cable isapplied to transfer the braking force to the brake device at the wheelside. Since the cable will tend to be extended when the applied tensionis too large when the braking lever is extremely pressed, the brakingdevice will not give enough braking force in this situation.

[0003] To solve the above problems, a disc brake system 100 has beendeveloped, as shown in FIG. 1. Braking fluid and the pipelines are usedas the medium of transmitting the brake force to the braking devices.When the rider pulls the lever of the braking device with a force 102,the piston 104 in the braking device pushes the braking fluid through aguide tube 106. The braking fluid is pressed into a brake member 108 ofthe braking device to pull out the friction pad 112 to impel a piston110 against a disc 114 of the brake member 108. The braking fluid, thesingle piston 104 and the piston 1 10 serve as transmission interface ofthe braking force in the disc brake system 100. A ratio offorce-enlargement is defined as magnifying rate of a force between thesingle piston 104 and the piston 110. There is a need to increase theratio of force-enlargement master cylinder.

[0004] If the cross-sectional area of the piston 104 and the piston 110is reduced, the ratio of the force-enlargement is increased, whichresults in a reduction of braking force applied on the rider's hand.However, such a situation of cross-sectional area decrement of thepiston 104 diminishes the flow rate of braking fluid in the piston 104and the displacement of the piston 110 is decreased and thus leaded intothe following drawbacks: (a) The piston 110 has an insufficient forwarddisplacement. Even if the piston 104 is entirely pushed down, the piston110 still cannot propel the friction pad 112 onto the brake disc 114,which leads to an inadequate force imposed on the braking system. (b)The piston 110 has an insufficient backward displacement. Even if thepiston 104 is totally released, the piston 110 with the friction pad 112still cannot be separated from the brake disc 114, which leads toabrasion, vibration, noise and human power dispersion.

[0005] Consequently, how to control the brake speed and the brakingforce of the braking device and how to increase the braking force andthe high ratio of force-enlargement are important problems and arecurrently main issues for braking device manufacturers of the bicycles.

SUMMARY OF THE INVENTION

[0006] The primary object of the present invention is that a frictionpad of a variable ratio of force-enlargement master cylinder rapidlyattaches to the disc of the brake member to increase the manipulation ofthe bicycle when a lever is dragged down in the beginning.

[0007] Another object of the present invention is that the friction padof the variable ratio of force-enlargement master cylinder is imposed ata higher normal force to increase the braking effect of vehicles.

[0008] According to the above objects, the present invention sets fortha variable ratio of force-enlargement master cylinder. The variableratio of force-enlargement master cylinder comprises a cylinder, anouter piston and an inner piston. The cylinder comprises a first cavitywhich includes a first opening, second opening and third opening on theperiphery of the first cavity. The first cavity is filled with fluidstored in a fluid supply device.

[0009] The first channel located inside a sidewall of the cylinder isconnected to the second opening with the third opening. The fluid in thefirst cavity is transmitted into the brake member by the first channelof the cylinder to apply pressure to the friction pad serving as animposition on the disc of the brake member.

[0010] The outer piston, hollow and cylindrical in shape, is coupled tothe first cavity of the cylinder by a first resilient body toreciprocate along the first cavity. The outer piston has a second cavityand a second channel inside a sidewall. The second cavity is connectedto the first cavity of cylinder via the second channel to fill thesecond cavity with the fluid. Moreover, the outer piston includes afourth opening and a fifth opening on the surface region of the outerpiston to drain the fluid outwardly. An annular recess is preferablypositioned on a surface region adjacent to the fourth opening of theouter piston to drain the fluid passing through the annular recess viathe first channel.

[0011] The inner piston coupled to the second cavity of the outer pistonis allowed to reciprocate with a second resilient body between the outerpiston and the inner piston along the second cavity. More significantly,the cross-section area of the inner piston is smaller than that of theouter piston along the axial center. When the rider applies force to theinner piston, the fluid stored in the first cavity of the cylinder isquickly exhausted at a higher speed to push the brake forward and thenthe friction pad is pressed onto the disc at a larger-than-normal force.In addition, the inner piston has a third channel therein to circulatethe fluid around the variable ratio of force-enlargement mastercylinder.

[0012] In the use of the variable ratio of force-enlargement mastercylinder, if a lever of the braking device is pulled, the outer pistoncompresses the fluid within the first cavity of the cylinder. Both sidesof the third channel are aligned with the second channel and the fourthopening of the outer piston, respectively. Also, the fifth opening isshielded with the sidewall of the cylinder so that the fluid passessequentially through the first cavity, the second channel, the thirdchannel and the fourth opening. Finally, the fluid exhausts from thefirst channel to transfer hydraulic pressure to the friction pad of thebrake member.

[0013] The friction pad of the braking member is propelled by the fluidwith a higher speed to serve as the step of “fast approaching”.Therefore, the friction pad rapidly contacts the disc to increase themanipulation of the bicycle.

[0014] If the rider continuously presses the lever, the outer pistonpropels the fluid within the first cavity until the bottom of the outerpiston contacts the bottom of the first cavity. Also, the third openingof the cylinder aligns with the fifth opening of the outer piston.Meanwhile, the fluid in the second cavity of the outer piston flowsthrough the fifth opening of the outer piston and the third opening ofthe cylinder. Afterward, the fluid later is drained away from the firstchannel of the cylinder.

[0015] In contrast with the step of fasting approaching, because theeffective cross-area of the inner piston is smaller than that of theouter piston, the fluid within the second cavity moves at a lower speedand at a higher pressure. Consequently, a higher pressure is transmittedinto the friction pad to increase the normal force applied to the disc,which is a step of “high pressure” to increase the variable ratio offorce-enlargement.

[0016] In summary, the variable ratio of force-enlargement mastercylinder makes the friction pad rapidly attach to the disc to reduce thebraking time. After the friction pad contacts the disc, the friction padcontinuously presses the disc at a higher-than-normal force to increasethe variable ratio of force-enlargement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing aspects and many of the attendant advantages ofthis invention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

[0018]FIG. 1 illustrates a brake disc of a bicycle device according tothe prior art;

[0019]FIG. 2 illustrates a cross-sectional view of a variable ratio offorce-enlargement master cylinder according to the present invention;

[0020]FIG. 3 illustrates a cross-sectional view of a variable ratio offorce-enlargement master cylinder whose fluid is transmitted at a higherspeed according to the present invention; and

[0021]FIG. 4 illustrates a cross-sectional view of a variable ratio offorce-enlargement master cylinder whose fluid is transmitted at a higherpressure according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The present invention is directed to a variable ratio offorce-enlargement master cylinder to improve the shortcomings of abraking device applied to bicycles in the prior art. A fluid filledwithin the variable ratio of force-enlargement master cylinder istransmitted into a brake member of the braking device to push a frictionpad so that the bicycle is effectively halted. The variable ratio offorce-enlargement master cylinder in the present invention is alsopreferably used to a variety of braking devices of vehicles.

[0023] The main theory of the variable ratio of force-enlargement mastercylinder in the present invention is based on some factors including abrake torque (T), a brake force between the friction pad and a disc, andthe equivalent brake radius of the friction pad on the disc, as shown inthe following equation:

T=Fr=(μN)r=μ(PA)r

[0024] where

[0025] T is the brake torque;

[0026] F is the brake force between the friction pad and the disc;

[0027] r is the equivalent friction radius of the friction pad opposedagainst the disc;

[0028] μ is the friction coefficient;

[0029] N is the normal force which the friction pad opposes against thedisc;

[0030] P is the fluid pressure imposed on pistons of the braking device;and

[0031] A are the effective area of the pistons.

[0032] In view of the above-mentioned, if the brake torque need to beenlarged, the value of these items including P, A, r, or μ must beincreased. However, μ is concerned with the material of the friction padand the disc and r is concerned with the size of the braking components.As a result, in the present invention, the A area of the pistons isallowed to be changed to vary the P pressure so that the pistons in thevariable ratio of force-enlargement master cylinder are sequentiallypropelled at a higher speed or variable ratio of force-enlargement. Inthe preferred embodiment of the present invention, two or more pistonsare used to improve the single piston of the prior art.

[0033]FIG. 2 shows a cross-sectional view of a variable ratio offorce-enlargement master cylinder according to the present invention.The variable ratio of force-enlargement master cylinder 200 comprises acylinder 202, an outer piston 204 and an inner piston 206. The cylinder202, a hollow column in shape, comprises a first cavity 208 whichincludes a first opening 210, second opening 212 and third opening 214on the periphery of the first cavity. The first cavity 208 is filledwith fluid stored in a fluid supply device 216, such as an oil bowl or achamber via the first opening.

[0034] A first channel 218 located inside a sidewall of the cylinder 202connects the second opening 212 with the third opening 214. The fluid inthe first cavity 208 is transmitted into a brake member by the firstchannel 218 of the cylinder 202 to apply pressure to the friction padserving as an imposition on the disc of the brake member.

[0035] The outer piston 204, hollow and cylindrical in shape, is coupledto the first cavity 208 of the cylinder 202 by a first resilient body224 to reciprocate along the first cavity 208. The first resilient body224, such as a compressible spring, preferably connects the bottom ofthe cylinder 202 with the bottom of the outer piston 204. The outerpiston 204 also has a second cavity 228 and a second channel 230 insidea sidewall of the outer piston 204. The second cavity 228 is connectedto the first cavity 208 of the cylinder 202 via the second channel 230to fill the second cavity 228 with the fluid. Moreover, the outer piston204 includes a fourth opening 232 and a fifth opening 234 on the surfaceregion of the outer piston 204 to drain the fluid outwardly. In thepreferred embodiment of the present invention, an annular recess 220 ispositioned on a surface region adjacent to the fourth opening 232 of theouter piston 204 to drain the fluid passing through the annular recess220 via the first channel 218 of the cylinder 202.

[0036] The inner piston 206, columnar, square, or the like in shape,which is coupled to the second cavity 228 of the outer piston 204, isallowed to reciprocate with a second resilient body 226 between theouter piston 204 and the inner piston 206 along the second cavity 228.The second resilient body 226, such as a compressible spring, preferablyconnects the bottom of the outer piston 204 with the bottom of the innerpiston 206. More importantly, the cross-section area 238 of the innerpiston 206 is smaller than cross-section area 240 of the outer piston204 along an axial center 236. When the rider applies a force to theinner piston 206, the fluid stored in the first cavity 208 of thecylinder 204 is quickly exhausted at a higher speed to push the frictionpad forward and then the friction pad is pressed onto the disc at alarger-than-normal force. In addition, the inner piston 206 has a thirdchannel 242 therein to circulate the fluid around the variable ratio offorce-enlargement master cylinder 200.

[0037] Furthermore, when the variable ratio of force-enlargement mastercylinder 200 is in an idle status, inactive brake, the fluid stored inthe fluid supply device 216 is injected into the first cavity 208 andflows the outer piston 204 and the third channel 242 of the inner piston206. Finally, the fluid is drained away from the first channel 218 ofthe outer piston 204. In other words, the fluid passes through the firstdirection 246 to communicate the fluid between the fluid supply device216 and the brake member to recover the stroke of the piston due to theabrasion of the friction pad.

[0038]FIG. 3 shows a cross-sectional view of the variable ratio offorce-enlargement master cylinder whose fluid is transmitted at a higherspeed according to the present invention. If a lever of the brakingdevice is pulled, the outer piston 204 compresses the fluid within thefirst cavity 208 of the cylinder 202. Both sides of the third channel242 are aligned with the second channel 230 and the fourth opening 232of the outer piston 204, respectively. Also, the fifth opening 234 isshielded with the sidewall of the cylinder 202 so that the fluid passessequentially through the first cavity 208, the second channel 230, thethird channel 242 and the fourth opening 232. Finally, the fluidexhausts from the first channel 218 to transfer hydraulic pressure tothe friction pad of the brake member.

[0039] Specifically, when the rider slightly pulls the lever, the firstcavity 208 is pressed by the cross-section area 240 of the outer pistonto increase the flow rate of the fluid passing through the first channel218. As a result, due to the higher fluid rate, the friction pad rapidlycomes near the disc to serve as a step of “fast approaching”. For thesame stroke of the lever, the friction pad is allowed to approach thedisc since the fluid exhausts at a high speed. Therefore, the frictionpad rapidly contacts the disc in the beginning to reduce greatly themovement of the lever, which increases the manipulation of the bicycle.

[0040] In the preferred embodiment of the present invention, a distanceof the annular recess 220 of the outer piston 204 along the axial center236 is equal to or more than that between the third opening 214 of thecylinder and the fifth opening 234 of the outer piston 204. In the “fastapproaching” step, the fluid passed through the fourth opening alwaysexhausts from the first channel 218 of the cylinder 202.

[0041] Additionally, in the preferred embodiment of the presentinvention, the fluid sequentially flows into the first cavity 208 andsecond cavity 228 to conserve sufficient fluid when the lever ispressed. Specifically, the fluid flows along the second direction 248.

[0042]FIG. 4 shows a cross-sectional view of a variable ratio offorce-enlargement master cylinder whose fluid is transmitted at a higherpressure according to the present invention. If the rider continuouslypulls the lever of the braking device, the outer piston 204 propels thefluid within the first cavity 208 until the bottom of the outer piston204 contacts the bottom of the first cavity 208. Also, the third opening214 of the cylinder 202 aligns with the fifth opening 234 of the outerpiston 204. Meanwhile, the fluid in the second cavity 228 of the outerpiston 204 flows through the fifth opening 234 of the outer piston 204and the third opening 214 of the cylinder 202. The fluid later isdrained away from the first channel 218 of the cylinder 202. In otherwords, the fluid flows along the third direction 250.

[0043] Therefore, after the friction pad attaches to the disc, the innerpiston 206 moves along the first cavity 208 of the outer piston 204 ifthe rider continuously imposes a force on the inner piston 206. Incontrast with the step of “fasting approaching”, the fluid within thesecond cavity 228 moves at a lower speed and at a higher pressurebecause the effective cross-area 238 of the inner piston 206 is smallerthan that 240 of the outer piston 206. Consequently, a higher pressureis transmitted into the friction pad to increase the normal forceapplied to the disc, which is a step of “high pressure” to increase thevariable ratio of force-enlargement.

[0044] According to the above-mentioned, when an rider pulls the leverof the bicycle, the outer piston of the variable ratio offorce-enlargement master cylinder is able to move rapidly so that thestroke of lever completes much early to reduce the brake time. After thefriction pad contacts the disc, the friction pad presses the disc at ahigher-than-normal force to increase the variable ratio offorce-enlargement. As a result, the present invention solves the problemof a long brake stroke and insufficient brake force.

[0045] As understood by a person skilled in the art, the foregoingpreferred embodiments of the present invention are illustrations ratherthan limitations of the present invention. It is intended that theycover various modifications and similar arrangements included within thespirit and scope of the appended claims, the scope of which should beaccorded the broadest interpretation so as to encompass all suchmodifications and similar structure.

What is claimed is:
 1. A variable ratio of force-enlargement mastercylinder for transmitting brake force into a braking device of a bicycleby a fluid to stop the bicycle, said variable ratio of force-enlargementmaster cylinder comprising: a cylinder having a first cavity, whereinthe first cavity includes a first opening, second opening and thirdopening therein, said first cavity is filled with the fluid via saidfirst opening, a first channel is positioned inside a sidewall of saidcylinder, and said first channel connects said second opening with saidthird opening for transmitting the brake force; an outer piston coupledto said first cavity of said cylinder by using a first resilient bodyfor reciprocal motion along said first cavity, said outer piston havinga second cavity and a second channel therein, said second cavityconnected to said first cavity of said cylinder via said second channelfor filling said second cavity with the fluid, said outer piston havinga fourth opening and a fifth opening thereon for draining the fluidoutwardly; and an inner piston coupled to said second cavity of saidouter piston by using a second resilient body for reciprocal motionalong said second cavity, and said inner piston having a third channeltherein for circulating the fluid around the braking device, a firstcross region of said inner piston being smaller than a second crossregion of said outer piston along an axial center.
 2. The variable ratioof force-enlargement master cylinder of claim 1, wherein said thirdchannel of said inner piston aligns with said second channel and saidfourth opening of said outer piston, respectively, and said fifthopening is shielded with the sidewall of said cylinder such that thefluid sequentially circulates into said second channel, said thirdchannel and fourth opening, and drains away via said first channel. 3.The variable ratio of force-enlargement master cylinder of claim 1,wherein said outer piston makes contact with an end of said first cavityof said cylinder and said third opening of said outer piston aligns withsaid fifth opening of said inner piston such that the fluid within saidsecond cavity of said outer piston sequentially circulates into saidfifth opening of said outer piston and said third opening of saidcylinder, and drains away via said first channel of said cylinder. 4.The variable ratio of force-enlargement master cylinder of claim 1,further comprising a fluid supply device connected to said first openingof said cylinder.
 5. The variable ratio of force-enlargement mastercylinder of claim 1, wherein said first resilient body comprises acompressible spring.
 6. The variable ratio of force-enlargement mastercylinder of claim 1, wherein said second resilient body comprises acompressible spring.
 7. The variable ratio of force-enlargement mastercylinder of claim 1, further comprising an annular recess in a surfaceof said outer piston.
 8. The variable ratio of force-enlargement mastercylinder of claim 7, wherein a first length of said annular recess ofsaid outer piston along the axial center is equal to a second lengthbetween said third opening of said cylinder and said fifth opening ofsaid outer piston along the axial center.
 9. The variable ratio offorce-enlargement master cylinder of claim 7, wherein a first length ofsaid annular recess of said outer piston along the axial center isgreater than a second length between said third opening of said cylinderand said fifth opening of said outer piston along the axial center. 10.A variable ratio of force-enlargement master cylinder for transmitting abrake force into a braking device by a fluid, said variable ratio offorce-enlargement master cylinder comprising: a cylinder having a firstcavity, wherein the first cavity includes a first opening, secondopening and third opening therein, said first cavity is filled with thefluid via said first opening, a first channel is positioned inside asidewall of said cylinder, and said first channel connects said secondopening with said third opening for transmitting the brake force; anouter piston coupled to said first cavity of said cylinder by using afirst resilient body for reciprocal motion along said first cavity, saidouter piston having a second cavity and a second channel therein, saidsecond cavity connected to said first cavity of said cylinder via saidsecond channel for filling said second cavity with the fluid, said outerpiston having a fourth opening and a fifth opening therein for drainingthe fluid outwardly; and an inner piston coupled to said second cavityof said outer piston by using a second resilient body for reciprocalmotion along said second cavity, said inner piston having a thirdchannel therein for circulating the fluid around the braking device, afirst cross region of said inner piston being smaller than a secondcross region of said outer piston along an axial center, said thirdchannel of said inner piston being aligned with said second channel andsaid fourth opening of said outer piston, respectively, and said fifthopening being shielded with the sidewall of said cylinder such that thefluid sequentially circulates into said second channel, said thirdchannel and fourth opening, and drains away via said first channel. 11.The variable ratio of force-enlargement master cylinder of claim 10,wherein said outer piston contacts an end of said first cavity of saidcylinder and said third opening of said outer piston aligns with saidfifth opening of said inner piston such that the fluid within saidsecond cavity of said outer piston sequentially circulates into saidfifth opening of said outer piston and said third opening of saidcylinder, and drains away via said first channel of said cylinder. 12.The variable ratio of force-enlargement master cylinder of claim 10,further comprising a fluid supply device connected to said first openingof said cylinder.
 13. The variable ratio of force-enlargement mastercylinder of claim 10, wherein said first resilient body comprises acompressible spring.
 14. The variable ratio of force-enlargement mastercylinder of claim 10, wherein said second resilient body comprises acompressible spring.
 15. The variable ratio of force-enlargement mastercylinder of claim 10, further comprising an annular recess on a surfaceof said outer piston.
 16. The variable ratio of force-enlargement mastercylinder of claim 15, wherein a first length of said annular recess ofsaid outer piston along the axial center is equal to a second lengthbetween said third opening of said cylinder and said fifth opening ofsaid outer piston along the axial center.
 17. The variable ratio offorce-enlargement master cylinder of claim 15, wherein a first length ofsaid annular recess of said outer piston along the axial center isgreater than a second length between said third opening of said cylinderand said fifth opening of said outer piston along the axial center.